The overall objective of the total project has been to obtain better understanding of the human enzyme system involved in alcohol metabolism. Our main purpose has been therefore to purify and characterize individual human alcohol dehydrogenase and aldehyde dehydrogenase isoenzymes. Purification of the human stomach alcohol dehydrogenase gamma gamma and human liver aldehyde dehydrogenase isoenzymes is now in progress. The gamma gamma isozyme is currently being characterized with regard to its kinetic properties with ethanol and acetaldehyde. Other human alcohol dehydrogenase isoenzymes will be purified and characterized when work on human gamma gamma isoenzyme is complete. Employing techniques of salt fractionation, ion exchange and affinity chromatography, we have obtained human liver aldehyde dehydrogenase of ca 20 percent purity, but are going to achieve 100 percent purity before characterization. Experimental work on alcohol dehydrogenase from various rat tissues and horse livers has been continued. Investigations in this laboratory have conclusively demonstrated that hepatocellular carcinoma from the rat contains another alcohol dehydrogenase with catalytic properties different from those of rat liver ADH. This new ADH isoenzyme is also present in the rat stomach lining, but absent from the rat fetal liver. The physiological significance of this new ADH isoenzyme is currently being investigated. Purification of horse liver ADH SS is now in its final stages. The enzyme is being characterized with regard to its interaction with coenzymes, substrates and inhibitors. Purification and characterization of polymorphic AA isoenzyme is planned in the future.